ONCE hailed as “Vacancies in space”, the dark patches in the Milky Way are testimony to the presence of dust which frustrated early optical astronomers. In the late Eighteen Century Willem Herschel first coined the phrase “holes in heaven” when he viewed dark markings surrounded by numerous stars. One of the most picturesque of these dark nebulae is a cloud toward the constellation Ophiuchus, shown in Figure 1, where it is now known that high concentrations of dust and molecular gas absorb practically all the visible light emitted from background stars. ...
Zie: Summary